Heat exchanger plate, a plate pack and a plate heat exchanger

ABSTRACT

The invention refers to a heat exchanger plate ( 4 ) for a plate heat exchanger ( 1 ), a plate package ( 3 ) and a plate exchanger ( 1 ). The plate ( 4 ) includes at least a first area ( 31 ) with a corrugation of ridges and valleys, the plurality of which extends in a first direction (A), and at least a second area ( 32 ) with a corrugation of ridges and valleys, the plurality of which extends in a second direction (B). The plate ( 4 ) has a central rotary axis extending in parallel with a normal line of the plate. The areas ( 31, 32 ) have a respective contour coinciding with a respective imaginary contour in a first rotary position of the plate with regard to the rotary axis and after a rotation 90° to a second rotary position of the plate with regard to the rotary axis.

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention refers to a heat exchanger plate for a plate heatexchanger, wherein the plate includes at least a first area with acorrugation of ridges and valleys, the plurality of which extends in afirst direction, wherein the plate has a central rotary axis whichextends in parallel with a normal line of the plate. The invention alsorefers to a plate package for a plate heat exchanger, and a plate heatexchanger.

Such heat exchanger plates for rotation a quarter of a round are knownfrom EP-A-165 179. The plates have a substantially square shape and forma plate package where the inlets and the outlets extend through thesides of the plate package, i. e. the heat exchanger media flow into andout of the plate package in a direction which is substantially parallelto the main extension plane of the plates. Each plate has four sideedges, wherein two opposite side edges are folded downwardly and the twoother opposite side edges are folded upwardly. Every second plate isrotated 90° in the plate package, wherein the downwardly folded sideedges of a plate abut the upwardly folded side edges of an adjacentplate, wherein these side edges are connected to each other by means ofa weld joint. In each corner of each plate a tab is formed, whichextends along a diagonal direction and in a plane that is substantiallyperpendicular to the extension plane of the plates.

The plates disclosed in EP-A-165 179 have an active heat exchangingsurface with a corrugation of ridges and valleys, which extend in adiagonal direction that is inclined 45° to the side edges of the plates.Due to reasons of the manufacturing technology, a corrugation may notextend to the side edges but there has to be an edge area in order toenable, for instance, bending of the edge. The edge area may inprinciple be only a substantially line-shaped bending area butpreferably the edge area has a substantially plane surface that has awidth of 10–15 mm. By such a corrugation the plate becomes very rigidwith regard to the shape in the diagonal direction, in which the ridgesand the valleys extend, but is significantly less rigid transversely tothe corrugation.

The plates are manufactured by compression moulding and when the platesare compressed for the shaping of the pattern, the material is extendedtransversally to the corrugation. When the press tool then is open andthe plate is released, a certain backspring is obtained due to theelasticity of the material. Since the main backspring occurs in thedirection in which the plate has the lowest shape rigidity thedeformation becomes relatively large. The original square plate thusobtains after the compression moulding a rhombic shape. Such a rhombicshape leads to poor pattern fitting of the adjacent plates in thecomplete plate package, which in turn leads to lower pressure strengthof the plate package.

SUMMARY OF THE INVENTION

The object of the present invention is to remedy the problems mentionedabove. In particular, it is aimed at a plate, at a plate package withsuch a plate, and a plate heat exchanger with such a plate package,wherein the plate package is designed to maintain its outer shape afterthe compression moulding. The maintaining of the outer shape after thecompression moulding. The maintaining of the outer shape after thecompression moulding is important during the joining of the plates withmodern welding methods such as laser beam welding.

This object is achieved by the plate initially defined, which ischaracterised in that the plate includes at least a second area with acorrugation of ridges and valleys, the plurality of which extends in asecond direction, wherein these areas have a respective contour, whichcoincides with a respective imaginary stationary contour in a firstrotary position of the plate with regard to said rotary axis and after arotation of 90° to a second rotary position of the plate with regard tothe rotary axis.

Since the heat exchanging surface includes two areas, which have acorrugation extending in a respective direction, the deformation of theshape in one of the areas may be counteracted by the deformation of theshape in the other area and vice versa. Consequently, the totaldeformation of the shape of the plate may be prevented or reduced andthe original outer shape may substantially be maintained also after thecompression moulding of the plate. The definition contour refers to theouter and inner contour of an area. One of said areas may for instancebe completely enclosed in another of said areas, wherein the border ofthe latter outer area to the inner area forms the inner contour of theouter area.

According to an embodiment of the invention, the area of said first areais substantially equal to the area of said second area. Furthermore, thefirst direction is advantageously perpendicular to the second direction.By such a design of the plate, the deformation of the shape may beprevented substantially completely.

According to a further embodiment of the invention, the plate includes adiagonal line, wherein the first direction is substantially parallel tothe diagonal line.

According to a further embodiment of the invention, the plate has acontour that coincides with an imaginary stationary contour in saidfirst rotary position and in said second rotary position. Such a contourinvolves for instance a circular or a polygonal shape with at least fourside edges, wherein the plate may have at least four corners and whereinsaid diagonal line extends between two opposite ones of said corners.

According to a further embodiment of the invention, the plate has anedge, which extends around the plate, and an edge area, which extendsaround the plate inside the edge. The total area of the edge area isrelatively small in relation to the area of said first and second areas,which form an active heat exchanging surface. Furthermore, the plate maybe substantially square and have four side edges, wherein two first ofsaid side edges are parallel and folded in a first direction along arespective folding line extending in said edge area in parallel with theside edge in question, wherein two second of said side edges areparallel and folded in a second direction along a respective foldingline extending in said edge area in parallel with the side edge inquestion, and wherein the first direction is opposite to the seconddirection.

According to a further embodiment of the invention, the plate includes asupport area, which extends around said first and second areas insidethe edge area and includes a corrugation of ridges and valleys. In sucha corrugated support area, the ridges and valleys may be given adirection that is favourable for the specific position in which theywill be located in the complete plate package so that the load isequalised between the different support points. By such a particularcorrugation for the support area, the number of support points in thisarea in the proximity of the side edges of the plate may besubstantially increased. At least a large number of the ridges andvalleys in the support area may thus extend in a direction whichdeviates from the diagonal direction of the ridges and valleys of theheat exchanging surface. The ridges and the valleys of the support areawill be shorter in their extension direction in comparison with theridges and valleys of the heat exchanging surface. Advantageously, theplate includes a marked border line between the heat exchanging surfaceand the support area.

According to an embodiment of the invention, the support area has ineach corner such a ridge or valley, which extends in a direction thatsubstantially coincides with a diagonal line between the corners.Furthermore, substantially each ridge and valley of the support areaalong a central part of the side edges may extend in a direction whichis substantially perpendicular to the side edge lying most closely tosaid ridge and valley. By such a design of the support area the numberof support points in this area may be iincreased with up to 50%. Theridges and the valleys in the support area may also have substantiallythe same spacing as the ridges and valleys of the heat exchangingsurface. Advantageously, the direction of the ridges and the valleys ofthe support area changes successively from the substantially diagonaldirection in the corners to the substantially perpendicular direction inthe central parts.

According to a further embodiment of the invention, the plate includesan extension plane, which extends in and in parallel to the edge area,wherein said valleys of the first and second areas are located at theextension plane and said ridges of the first and second areas arelocated above the extension plane. Said valleys of the support area mayadvantageously be located below the extension plane and said ridges ofthe support area above the extension plane.

The object is also achieved by a plate package for a plate heatexchanger, which includes a number of plates arranged on each other asdefined above. The plates in the plate package may advantageously bearranged in such a way that every second plate is rotated 90° aroundsaid rotary axis and in such a way that interspaces are formed betweenadjacent plates, wherein said first and second areas have such a shapethat the contour of the first area coincides for all plates in the platepackage and that the contour of the second area coincides for all platesin the plate package. Furthermore, the plates in the plate package maybe welded to each other, wherein the plates are arranged on each otherin such a way, that said first side edges of a plate abut said secondside edges of an adjacent plate, and wherein these side edges areconnected to each other by means of a weld joint. Substantially allplates in the plate package may be substantially identical. Furthermore,said interspaces may include a number of first interspaces and a numberof second interspaces, wherein the first interspaces are arranged toconvey a first medium through the plate package and the secondinterspaces are arranged to convey a second medium through the platepackage.

The object is also achieved by a plate heat exchanger including a plateas defined above.

The object is also achieved by a plate heat exchanger including a platepackage as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now to be explained more closely by adescription of various embodiments disclosed by way of example and withreference to the drawings attached hereto.

FIG. 1 discloses a side view of a plate heat exchanger.

FIG. 2 discloses a sectional view along the line II—II in FIG. 1.

FIG. 3 discloses a sectional view along the line III—III in FIG. 2.

FIG. 4 discloses a plan view of a plate package of the plate heatexchanger.

FIG. 5 discloses a sectional view along the line V—V in FIG. 4.

FIG. 6 discloses a sectional view along the line VI—VI in FIG. 4.

FIG. 7 discloses a sectional view along the line VII—VII in FIG. 4.

FIG. 8 discloses a plan view of a plate according to a secondembodiment.

FIG. 9 discloses a plan view of a plate according to a third embodiment.

FIG. 10 discloses a plan view of a plate according to a fourthembodiment.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

FIGS. 1–3 disclose a plate heat exchanger 1. The plate heat exchanger 1includes an outer casing 2 and a plate package 3, which is arrangedinside the casing 2. The plate package 3 includes a number of heatexchanger plates 4 which are stacked on and attached to each other.

The plates 4 have a central rotary axis x, which extends in parallelwith a normal line of a main extension plane p of each plate 4. Allplates 4 are substantially identical and have in the embodimentdisclosed a substantially square shape with four corners. It is to benoted that the plates 4 also may have another polygonal or circularshape. The plates 4 are rotatable around the axis x in such a way thatthe outer contour of the plates 4 coincides with an imaginary stationarycontour in a first rotary positioned and after rotation 90° to a secondrotary position.

Each plate 4 has a heat exchanging surface 5 with a corrugation ofridges and valleys, see FIG. 4. Each plate 4 also has an edge, whichextends round the plate 4, and a substantially line-shaped orsurface-shaped edge area 6, which extends around the heat exchangingsurface 5 inside the edge. In the embodiment disclosed, the edge formsfour side edges 7′, 7″. Two 7′ of the side edges are parallel to eachother and folded downwardly in a first direction along a respectivefolding line that extends in the edge area 6 in parallel with the sideedge 7′ in question. The two second 7″ side edges are also parallel toeach other and folded upwardly in a second opposite direction along arespective folding line extending in the edge area 6 in parallel withthe side edge 7″ in question. In each corner of each plate 4 a tab 8 isformed when folding the side edges, which extends along a diagonaldirection and in a plane which is substantially perpendicular to theextension plane p of the plates 4. These tabs 8 function as attachmentmembers for mounting the plates 4 and the plate package 3 in the casing2. More specifically, the tabs 8 are directly or indirectly attached inlongitudinal groves in four corner posts 9 which are arranged in arespective corner in the inner space of the casing 2. The corner posts 9also function to delimit four part spaces 10 between the casing 2 andthe plate package 3.

Every second plate 4 in the plate package 3 is rotated 90° around therotary axis x, wherein the plates 4 are arranged in the plate package 3in such a way that interspaces 13′, 13″ are formed between adjacentplates 4 and that the first side edges 7′ of a plate 4 abut the secondside edges 7″ of an adjacent plate 4. The adjacent side edges 7′ and 7″are attached to each other by means of a weld joint 14, see FIG. 7. Theweld joint 14 may be obtained by means of laser beam welding or electronbeam welding. The interspaces 13′, 13″ include a number of firstinterspaces 13′ and a number of second interspaces 13″, see FIGS. 4–7.In such a way, the plate package 3, seen from two opposite sides, willbe open with regard to the first interspaces 13′ and closed with regardto the second interspaces 13″. Seen from the two other opposite sides,the plate package 3 will be closed with regard to the first interspaces13′ and opened with regard to the second interspaces 13″. The firstinterspaces 13′ are arranged to convey a first medium through the platepackage 3 and second interspaces 13″ are arranged to convey a secondmedium through the plate package 3.

The plate heat exchanger 1 includes a first inlet 16 and a first outlet17 for the first medium, and a second inlet 18 and a second outlet 19for the second medium. The inlets and the outlets to the plate package 3proper extend though the sides of the plate package 3, i. e. the heatexchanger media flow into and out of the plate package 3 in a directionthat is substantially parallel to the main extension plane p of theplates 4. In the embodiment disclosed, the plate package 3 includesthree part packages a, b, c. The part packages a, b, c are delimitedfrom each other by means of two delimiting plates 21, 22. It is to benoted that the plate package 3 may include another number of partpackages, for instance 1, 2, 4 or more such part packages.

In the embodiment disclosed, the first medium is conveyed in through thefirst inlet 16 into the part package a through one side to the firstinterspaces 13′. The first medium leaves the part package a through theopposite side and is conveyed into the part space 10. In the part space10, the first media is conveyed passing the delimiting plate 21 and intothe part package b through a side to the first interspaces 13′. Themedia leaves the part package b through the opposite side and enters theopposite part space 10. In this part space 10 the first media isconveyed passing the second delimiting plate 22 and into the partpackage c through the side to the first interspaces 13′. Thereafter, thefirst media leaves to plate heat exchanger 1 via the opposite side ofthe part package c, the part space 10 and the second outlet 17. In acorresponding manner the second media is conveyed into the first inlet18 through the plate heat exchanger 1 and via the second inlet 19. It isto be noted that the second media also may be conveyed in counterflow tothe first media in such a way that the outlet 19 forms an inlet and theinlet 18 an outlet.

The heat exchanging surface 5 includes in the embodiment disclosed inFIG. 4 a first area 31 with a corrugation of ridges and valleys, and asecond area 31 with a corrugation of ridges and valleys. The valleys ofboth the areas 31, 32 of the heat exchanging surface 5 are located at orat the level of the extension plane p and the ridges of both the areas31, 32 of the heat exchanging surface 5 are located above the extensionplane p.

The ridges and the valleys in the first area 31 extend in a firstdirection A, and the ridges and the valleys in the second area extend ina second direction B. The first direction A is substantiallyperpendicular to the second direction B. Furthermore, the firstdirection A is substantially parallel to a diagonal line extendingbetween two opposite corners of the plate 4, and the second direction Bis parallel to a diagonal line extending between the other two oppositecorners of the plate 4. It is to be noted that the ridges and thevalleys of the areas 31, 32 of the heat exchanging surface 5 may extendalong other directions than those disclosed. The ridges and valleys inthe first area 31 do not need to extend perpendicularly to the ridgesand valleys in the second area 32 but it is important that the ridgesand valleys in the first area 31 form an angle to the ridges and valleysin the second area 32. The ridges and valleys of the areas 31, 32 of theheat exchanging surface 5 may also extend along curved path and havelarger or smaller interruptions or irregularities, for instance in orderto form support points in relation to adjacent surfaces or in order toinfluence the flow through the plate heat exchanger 1. Inserted portionswith deviating patterns may also be present for other reasons.

The area of the first area 31 is substantially equal to the area of thesecond area 32. Each of the areas 31, 32 also has an outer and/or innercontour which coincides with a respective imaginary stationary contourin the first rotary position of the plate 4 with regard to the rotaryaxis x and after a rotation of 90° to the second rotary position of theplate 4 with regard to the rotary axis x. The second inner area 32 issquare and rotated 45° in relation to the first outer area 31, whichalso is square. The outer contour of the inner area 32 forms orcoincides with the inner contour of the outer area 31. In the platepackage 4 a ridge of the heat exchanging surface 5 will substantiallyalways abut a valley of the heat exchanging surface 5 of an adjacentplate 4, wherein this ridge crosses this valley in such a way that asupport point or a small support area is formed.

Each plate 4 includes a support area 41, which extends around the heatexchanging surface 5 inside the edge area 6. The support area 41 alsoincludes a corrugation of ridges 42 and valleys 43. The border betweenthe support area 41 and the heat exchanging surface 5 is marked with aborder line 44 that is located at or at the level of the extension planep. The valleys 43 of the support area 41 are located below the extensionplane p and the ridges 42 of the support area 41 are located above theextension plane p.

In the proximity of each corner, the support area 41 has such a ridge 42or valley 43 extending in a direction that substantially coincide with adiagonal line between the corners. Along a central part of the sideedges, substantially each ridge 42 and valley 43 of the support area 41extends inside one of the side edges in a direction which issubstantially perpendicular to the side edge which lies most closely tosaid ridge 42 and valley 43. The direction of the ridges 42 and thevalleys 43 of the support area 41 changes successively from the diagonaldirection in the corners to the perpendicular direction in the centralparts.

The ridges 42 and the valleys 43 of the support area 41 are thuspositioned in such a way that each valley 43 in the support area 41 of aplate 4 abuts a ridge 42 in the support area of a plate 4 lyingtherebelow, see FIGS. 6 and 7. In such a way support lines, or elongatedsupport surfaces, will always be formed between all adjacent plates 4 inthe plate package 3, which support lines extend in the directions of theridges 42 and the valleys 43. Also the support area 41 has such a shapethat the outer and inner contour of the support area 41 coincide for allplates 4 in the plate package 3.

FIG. 8 discloses a plate 4 with a heat exchanging surface 5 which isdivided in into two areas 31, 32 according to a second embodiment. Theinner area 32 is shaped as a square that is positioned in such a waythat the side edges of the outer contour of the inner area 32 extend inparallel to the most closely lying side edges of the outer contour ofthe outer area 31.

FIG. 9 discloses a plate 4 with a heat exchanging surface 5 that isdivided into two areas 31, 32 according to a third embodiment. The innerarea 32 is shaped as a circle that is positioned in such a way that thecentre point of the circle coincides with the centre point of the outerarea 31.

FIG. 10 discloses a plate 4 with a heat exchanging surface 5 which isdivided into a plurality of areas according to a fourth embodiment. Theplate 4 has two mains areas 31, 32, wherein one of the main areas 31includes a central square area 33 and four triangular corner areas 34,one in each corner.

All plates according to FIGS. 8–10 are as the plate in FIG. 4 alsoshaped in such a way that each area 31, 32, 33, 34 has a respectiveouter and/or inner contour, which coincide with a respective imaginarystationary contour in the above-mentioned first rotary position of theplate 4 with regard to the rotary axis x, and after a rotation of 90° tothe above-mentioned second rotary position of the plate 4 with regard tothe rotary axis x. The total area of one of the areas 31, or the mainarea 31, is substantially equal to the total area of the other area 32,or the main area 32.

It is to be noted that the support area 41 is not indicated in FIGS.8–10, but these embodiments may of course also include a support area 41of the type described above.

The invention is not limited to the embodiments disclosed but may bevaried and modified within the scope of the following claims.

It is to be noted that the invention also is applicable to plates thatlack the disclosed support area 41.

1. A heat exchanger plate for a plate heat exchanger, having at least afirst area with a corrugation of ridges and valleys, the plurality ofwhich extends in a first direction, the plate having a central rotaryaxis (x) which extends in parallel with a normal line of the plate, andthe plate including at least a second area with a corrugation of ridgesand valleys, the plurality of which extends in a second direction, saidfirst and second areas having a respective contour, coinciding with arespective imaginary stationary contour in a first rotary position ofthe plate with regard to said rotary axis (x) and after a rotation of90° to a second rotary position of the plate with regard to the rotaryaxis (x), wherein the plate has an edge, which extends around the plate,and an edge area, which extends around the plate inside the edge, and issubstantially square and has four side edges and four corners, whereinfirst two of said side edges are parallel and folded in a firstdirection along a respective folding line extending in said edge area inparallel with the side edge in question, wherein second two of said sideedges are parallel and folded in a second direction along a respectivefolding line extending in said edge area in parallel with the side edgein question, and wherein the first direction is opposite to the seconddirection.
 2. A plate according to claim 1, wherein the area of saidfirst area is substantially equal to the area of said second area.
 3. Aplate according to claim 1, wherein the first direction is substantiallyperpendicular to the second direction.
 4. A plate according to claim 1,wherein the plate includes a diagonal line, wherein the first directionis substantially parallel to the diagonal line.
 5. A plate according toclaim 1, wherein the plate has a contour that coincides with animaginary stationary contour in said first rotary position and in saidsecond rotary position.
 6. A plate according to claim 4, wherein saiddiagonal line extends between two opposite ones of said corners.
 7. Aplate according to claim 1, wherein the plate, includes a support area,which extends around said first and second areas inside the edge areaand includes a corrugation of ridges and valleys.
 8. A plate accordingto claim 7, wherein the plate includes a marked border line between thesupport area and said first and second areas.
 9. A plate according toclaim 8, wherein in each corner the support area has such a ridge orvalley, which extends in a direction that substantially coincides with adiagonal line between the corners.
 10. A plate according to claim 8,wherein substantially each ridge and valley of the support area along acentral part of the side edges extends in a direction that issubstantially perpendicular to the side edge lying most closely to saidridge and valley.
 11. A plate according to claim 10, wherein thedirection of the ridges and the valleys of the support area changessuccessively from the diagonal direction in the corner to theperpendicular direction in the central part.
 12. A plate according toclaim 7, wherein the plate includes an extension plane (p), whichextends in and in parallel to the edge area, wherein said valleys of thefirst and second areas are located at the extension plane (p) and saidridges of the first and second areas are located above the extensionplane (p).
 13. A plate according to claim 12, wherein said valleys ofthe support area are located below the extension plane (p) and saidridges of the support area are located above the extension plane (p).14. A plate package for a plate heat exchanger, wherein the platepackage includes a number of substantially square plates each havingfour corners and at least a first area with a corrugation of ridges andvalleys, the plurality of which extends in a first direction, the plateshaving a central rotary axis (x) which extends in parallel with a normalline of the plates, and each plate including at least a second area witha corrugation of ridges and valleys, the plurality of which extends in asecond direction, the first direction and the second direction formingan angle greater than zero and less than 180 degrees with respect to oneanother, said first and second areas having a respective contour,coinciding with a respective imaginary stationary contour in a firstrotary position of the plates with regard to said rotary axis (x) andafter a rotation of 90° to a second rotary position of the plates withregard to the rotary axis (x), said plates being arranged on each other,wherein the plates in the plate package are arranged in such a way thatevery second plate is rotated 90° around said rotary axis (x) and insuch a way that interspaces are formed between adjacent plates, whereinsaid first and second areas have such a shape that the contour of thefirst areas coincides for all plates in the plate package and that thecontour of the second areas coincides for all plates in the platepackage and wherein the plates in the plate package are welded to eachother.
 15. A plate package according to claim 14 wherein the plates havean edge around the plate and have an edge area that extends around eachplate inside its edges and have four side edges, a first two of saidside edges being parallel and folded in a first direction along arespective folding line extending in said edge area in parallel with theside edge in question, a second two of said side edges being paralleland folded in a second direction along a respective folding lineextending in said edge area in parallel with the side edge in question,wherein the first direction is opposite to the second direction, whereinthe plates are arranged on each other in such a way that first sideedges of a plate abut said second side edges of an adjacent plate andwherein the abutting side edges are connected to each other by means ofa weld joint.
 16. A plate package according to claim 15, wherein theplates include a support area which extends around said first and secondareas inside the edge area and includes a corrugation of ridges andvalleys.
 17. A plate package according to claim 16, wherein the platesinclude a marked border line between the support area and said first andsecond areas.
 18. A plate package according to claim 17, wherein in eachcorner the support area has such a ridge or valley, which extends in adirection that substantially coincides with a diagonal line between thecorners.
 19. A plate package according to claim 17, whereinsubstantially each ridge and valley of the support area along a centralpart of the side edges extends in a direction that is substantiallyperpendicular to the side edge lying most closely to said ridge andvalley.
 20. A plate package according to claim 19, wherein the directionof the ridges and the valleys of the support area changes successivelyfrom the diagonal direction in the corner to the perpendicular directionin the central part.
 21. A plate package according to claim 16, whereinthe plates include an extension plane (p), which extends in and inparallel to the edge area, wherein said valleys of the first and secondareas are located at the extension plane (p) and said ridges of thefirst and second areas are located above the extension plane (p).
 22. Aplate package according to claim 21, wherein said valleys of the supportarea are located below the extension plane (p) and said ridges of thesupport area are located above the extension plane (p).
 23. A platepackage according to claim 14, wherein substantially all plates aresubstantially identical.
 24. A plate package according to claim 14,wherein said interspaces include a number of first interspaces and anumber of second interspaces, wherein the first interspaces are arrangedto convey a first medium through the plate package and the secondinterspaces are arranged to convey a second medium through the platepackage.
 25. A plate heat exchanger, wherein the plate heat exchangerincludes a plate package according to claim
 14. 26. A plate packageaccording to claim 14, wherein the area of said first area issubstantially equal to the area of said second area.
 27. A plate packageaccording to claim 14, wherein the first direction is substantiallyperpendicular to the second direction.
 28. A plate package according toclaim 14, wherein the plates include a diagonal line and wherein thefirst direction is substantially parallel to the diagonal line.
 29. Aplate package according to claim 14, wherein the plates have a contourthat coincides with an imaginary stationary contour in said first rotaryposition and in said second rotary position.
 30. A plate packageaccording to claim 28, wherein the diagonal line extends between twoopposite corners of the plates.